Large studies demonstrated that moderate or severe patient-prosthesis mismatch (PPM) occurs in 44.2% to 65% of patients undergoing aortic valve replacement. If there is general agreement that patients with PPM have worse outcome than patients without, it is difficult to understand how to prevent this dangerous complication. The formula used to calculate the effective orifice area (EOA) of an implanted aortic prosthesis has many weak points that produce inconsistent results using the same prosthetic valve (type and size). The observed EOA (3 to 6 months postoperatively) of a #23 biological prosthesis can range from 0.9 to 3.5 cm², making PPM prevention impossible using projected EOA, where only the mean value is reported (1.83 cm² for the same #23 biological prosthesis). An EACTS-STS-AATS Valve Labelling Task Force has been established to suggest the manufacturers to present essential information on valvular prosthesis characteristics in standardized Valve Charts. For valves used in the aortic position, Valve Charts should include a standardized PPM chart to assess the probability of PPM after implantation. This will not solve completely the conundrum of prevention, but most likely it will be a step ahead.